> I am confident that authorities (and insurance companies), will want to apportion blame.
In general this isn't how airline investigations actually work. They instead use the concept of "just cause" meaning that the assumption is that the system failed, and that any mistake is the child of many parents, none whom are at fault on their own. This is why flying is so safe, no one in the entire system is afraid to report failures or mistakes because the assumption is to get better, not to punish why something is bad.
There may be a single final failure but why did was the system set up to allow that to happen at all in the first place is the question. In this case there will certainly be investigations at every level from the flight crew and cabin crew training, to their sleep schedule, to the forecasts, to the flight path planning, to the policies around passengers moving around the cabin, to even how the plane was balanced on passenger and cargo loading. There's going to be a combination of factors no doubt, but no one's going to get fired (some individuals may resign or retire from the stress of handling such a situation, which no one would fault them for). Singapore just got voted the #1 airline in the world, they will take this as seriously as if the entire plane went down.
These findings will then be applied to every major airline and aircraft in the world so that it never happens again. With a few very public recent incidents, any specific type of airline accident tends to happen only once.